Port fuel injected engines receive fuel pumped from a fuel tank via a fuel pump. The fuel pump supplies fuel to a fuel rail, and fuel injectors coupled to the fuel rail inject fuel into engine intake ports. Fuel may be delivered to the engine from the fuel rail as liquid, gas, or a mixture of gas and liquid depending on a state of the fuel in the fuel rail. However, injecting fuel in a liquid state may be more desirable since the amount of fuel injected may be more easily controlled. Injection of liquid fuel may be ensured by increasing fuel pressure above the fuel's vapor pressure. The fuel pressure may be increased by supplying additional energy to the fuel pump. However, increasing the amount of energy supplied to the fuel pump may decrease vehicle fuel economy since energy to operate the fuel pump is derived from an alternator that is coupled to the vehicle's engine. Additionally, a pressure at which fuel may be delivered to the engine in a liquid state may vary with fuel composition and fuel temperature. Consequently, it may be difficult to provide fuel to an engine in a liquid state without delivering it at a pressure that increases vehicle fuel consumption more than is desired.
The inventors herein have recognized the above-mentioned limitations and have developed a method for fueling an engine, comprising: receiving fuel data to a controller; estimating fuel compressibility from the fuel data via instructions in the controller; and adjusting output of a fuel pump via the controller in response to the estimated fuel compressibility.
By adjusting output of a fuel pump responsive to fuel compressibility, it may be possible to provide the technical result of supplying liquid fuel to an engine while reducing power supplied to a fuel pump. In particular, the fuel's compressibility may provide a basis for regulating fuel pressure supplied to the engine so that liquid fuel may be provided to the engine while minimizing fuel pump energy consumption. Fuel pump output may be increased or decreased responsive to the fuel's compressibility. Consequently, even when fuel properties that affect state of a fuel being injected are unknown, fuel may be injected to the engine in a liquid state while minimizing fuel pump energy consumption.
The present description may provide several advantages. In particular, the approach may provide for supplying liquid fuel to an engine at reduced fuel pump outlet pressures. The reduced pressure is particularly useful for extending the injector's dynamic range to being able to accurately accommodate small fuel injection masses. The small fuel injection mass is important at idle conditions with fuel vapor purge operating. This action does not reduce the ability to provide standard pressure (or higher pressure) at high engine speed when the injection window is short. High engine speed is a less frequent condition, and therefore, high pressure during this condition does not substantially affect fuel economy. In addition, the method provides for adjusting fuel pressure supplied to an engine without knowledge of fuel type or fuel vapor pressure. Further, the approach provides for controlling energy supplied to a fuel pump without knowledge of fuel vapor pressure or fuel temperature.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.